The rough edges of small plastic parts may be polished by a process known as abrasive tumbling. The parts are placed in a rotating chamber together with an abrasive medium, and the mixing of the medium and the parts will smooth and polish the parts. During the tumbling process, a static electrical charge often builds up on the tumbling chamber, the medium and the tumbled parts. If the parts are relatively large, this does not cause any significant problem. However, if the parts are very small, the static charge can tend to repell the small plastic parts out of the abrasive medium so as to defeat the purpose of the tumbling process.
Very small plastic parts are used for devices known as intraocular lenses. It is commonly accepted that the vision-impairing disease known as cataracts can be alleviated by surgically replacing the natural lens of the eye with an artificial intraocular lens. Intraocular lenses have two principal parts: a medial, light-focusing body (also known as the optic) made of a non-toxic, plastic material which will replace the natural lens of the eye and focus light on the retina. Certain types of intraocular lenses include plastic supports (also known as haptics) which extend from the optic to the anatomy of the eye and provide means for fixing and holding the optic in proper position within the eye. These haptic supports can be made of tiny filaments of flexible, memory-retaining plastic, for example, polypropylene or some other plastic fibrous material attached to the optic by a variety of methods. Holes can be drilled into the edge of the optic, and the end of the haptic filament can be bonded, glued or crimped into these holes. There are a variety of other methods for attaching the haptics to the optic.
A well-known lens in which small haptic filaments are affixed to the optic is shown in U.S. Pat. No. 4,159,546. This lens is popularly known as the Shearing or J-loop lens. Such a lens is shown in FIG. 1 of the present invention wherein the optic is designated by reference character 1, and the haptic filaments are designated as reference characters 2 and 3. The diameter of the haptic filaments can be as small as 0.006 inches, and the length of the haptic filaments can be in the vicinity of 6 millimeters.
Before these haptic filaments are attached to the optic, any sharp edges must be polished away to minimize irritation to the internal anatomy of the eye. One process for providing this polishing is to tumble the filaments in an abrasive medium. Because the filaments are so small and light, the static electrical charge which they tend to pick up during tumbling can cause the filaments to migrate out of the tumbling medium and either float freely in the tumbling chamber or cling to the interior wall of the chamber.
It would be desirable to have an apparatus and a method for dissipating the static electrical discharge that may build up on the tumbling medium and the haptic filaments so that the haptic filaments will tend to stay within the tumbling medium and be properly smoothed and rounded.